1. Field of the Invention
The present invention relates to a blade mounted on various work machines such as a bulldozer and a tractor shovel, and more particularly, to a compact blade apparatus of a work machine and a work machine including the blade apparatus, the blade apparatus being suitable for operation such as digging, transporting and leveling, and having excellent assembling performance, workability, fuel economy and cost efficiency.
2. Description of the Related Art
In various workplaces such as construction workplace and civil engineering workplace, various work machines such as a bulldozer and a tractor shovel are used heavily. On the work machine of this kind, a blade which is a work implement is mounted. This blade is widely used for dozer operation such as digging, transporting, piling, compaction and leveling.
To fully exploit the best operation efficiency in this work machine, it is important to increase the amount of transported soil per one cycle as much as possible, to reduce resistance caused during digging and transporting as small as possible, and to satisfy various conditions such as compatibility between various soil characteristics. If the work machine can also carry out the piling, compaction and leveling, it is preferable because the operation efficiency is remarkably enhanced. If the optimal structure, shape, width and height of the blade as well as position of a cutting edge and digging angle which satisfy these conditions can be found, there are merits that the operation efficiency of the work machine is enhanced, the fuel consumption is reduced, and the entire work period can be shortened. When the optimal structure and the like are found, it is also necessary that the blade can be produced easily and inexpensively.
Japanese Patent No. 2757135 (patent document 1) discloses one example of the blade for increasing workload of the work machine of this kind. According to this publication, when soil is to be transported, an attitude of the blade provided on a large bulldozer is pitched back through a predetermined angle with respect to an attitude of the blade at the time of digging by a blade control apparatus, thereby increasing an amount of soil held in the blade, and when soil is to be discharged, the attitude of the blade is pitched dump through a predetermined angle with respect to the attitude of the blade at the time of digging so that soil discharging operation is facilitated.
To fully exploit the operation efficiency of a bulldozer, a balance between forces in the transporting operation of the bulldozer must be set such that tractional force is greater than transporting resistance and driving force of the vehicle is greater than the tractional force. In the bulldozer of the patent document 1, the tractional force is increased and the transporting resistance is reduced and the workload of the bulldozer is increased by controlling the attitude of the blade, as described above. Nevertheless, it makes it possible to largely increase the transporting amount without increasing the bulldozer in size, increasing the engine output or increasing the capacity of the blade.
Most of the engine output required when the bulldozer carries out digging and transporting operations is consumed for the driving force of the vehicle and the tractional force when the digging and transporting operations are carried out. Therefore, it is also necessary to reduce the loss of energy amount during power transmission and to enhance the fuel consumption efficiency. If these requirements are satisfied, it becomes possible to effectively use the engine output during the digging and transporting even if the blade has the same capacity as that of the conventional technique and the tractional force is the same as that of the conventional technique.
The present applicant proposed a totally new blade structure for satisfying the above requirements in WO2004-044337A1 (patent document 2).
The blade disclosed in this patent document 2 includes a central front surface portion, and a connecting front surface portion and an end front surface portion which are bent and continuously provided on each of right and left ends of the central front surface portion in succession. The central front surface portion has a blade width whose lower end intersects a digging direction and extends in the lateral direction, and is provided at a further lower end of said lower end with a first cutting edge. The connecting front surface portion is disposed on each of the right and left ends of the central front surface portion, and is provided at a lower end of the connecting front surface portion with a second cutting edge. The end front surface portion is continuously provided on the connecting portion, and is provided at a lower end of the end front surface portion with a third cutting edge. A cross line between the connecting front surface portion and the end front surface portion and a cross point between blade edges of the second cutting edge and the third cutting edge are located on a retreat position retreated from the blade edge of the first cutting edge as viewed from above. Front surfaces of the central front surface portion, the connecting front surface portion and the end front surface portion have special shapes formed in a concavely curved surface which is continuous from an upper end to a lower end.
A construction machine and an earthmoving machine are included as a work machine to which the blade of the patent document 2 is applied. Typical examples of the construction machine and the earthmoving machine include a construction vehicle and an earthmoving vehicle such as a bulldozer, a backhoe and a motor grader. The terms “as viewed from front” and “as viewed from above” of the blade of the present invention are used in this specification based on the condition that the blade is put on the earth's surface at an digging angle of highest digging efficiency.
The blade of the patent document 2 is the same as a conventional blade in that the blade includes a central front surface portion constituting a portion of a blade front surface, and right and left end front surface portions expanding such as to open forward at right and left side ends of the blade. However, the blade of the patent document 2 is largely different from the conventional blade in that the right and left end front surface portions extend through right and left connecting front surface portions which are continuously disposed from the right and left ends of the central front surface portion such as to open rearward, and front surface portions of all of the central front surface portion, the connecting front surface portion and the end front surface portion are curved in a concave manner from the upper end to the lower end.
In the entire blade, its first cutting edge positively cuts earth and sand substantially earlier than the third cutting edge of the end front surface portion. Therefore, digging force of the third cutting edge of the end front surface portion is smaller than that of the conventional blade end. Thus, as compared with the conventional blade, the tractional force applied to the cutting edge of the end front surface portion is moderated, resistance force such as digging resistance and transporting resistance are transmitted to the first cutting edge and the third cutting edge of the end front surface portion substantially uniformly.
In the case of the blade of the patent document 2, the tractional force is effectively applied to both the first cutting edge and the cutting edge of the end front surface portion, soil cut by the third cutting edge of the end front surface portion and soil cut by the first cutting edge of the central front surface portion smoothly merge with each other. As a result, as compared with the conventional blade provided at right and left portions of its blade body with blade plates, the resistance force is largely reduced, and the amount of soil per tractional force can largely be increased. Further, consumed horsepower during digging and transporting can largely be reduced, it is possible to obtain the maximum digging and transporting amounts within short time and with minimum energy amount, the fuel economy efficiency of the work machine is remarkably enhanced, and cost per earthwork amount can be reduced.
The outward appearance shape of soil when soil is pushed by the blade of the patent document 2 is such that the central front surface portion is largely swelled forward from its upper end toward its lower end, and its central portion exceeds the angle of repose. On the other hand, in the case of the conventional blade, the outward appearance shape of the soil is such that the blade is straight and flat surface shape having an inclination angle that is substantially equal to the angle of repose from the upper end toward the lower end of the blade.
The resistance is reduced by the synergism, and the amount of soil per tractional force can largely be increased. Further, the consumed horsepower during digging and transporting can largely be reduced, it is possible to obtain the maximum digging and transporting amounts within short time and with minimum energy amount, the fuel economy efficiency of the work machine is remarkably enhanced, and cost per earthwork amount can be reduced.
The second cutting edge and the third cutting edge are continuous with each other in a V-shape or U-shape. Especially when cohesion of soil is high, if the second cutting edge and the third cutting edge are connected to each other in the V-shape, the excavated soil is attached to a switching portion between the connecting front surface portion and the end front surface portion and agglomerated in many cases. Therefore, it is preferable that the switching portion is curved into U-shape. Further, blade front surfaces of the central front surface portion, the connecting front surface portion and the end front surface portion are vertically continuously curved surfaces, and these curved surfaces are concave surfaces having the same curvature. If the surfaces are formed into the curved surfaces in this manner, a large amount of soil can be carried on the blade front surface of the respective front surface portions, excellent balance of ground pressure in the front and rear portions of the vehicle body can be obtained, power loss such as shoe slip is small, and high tractional force can be obtained. It is also possible to prevent soil accumulated on the blade front surface of the respective front surface portions of the blade from exceeding the upper ends of the respective front surface portions and from overflowing rearward.
Since the blade is prone to be large in size and heavy in weight, a sheet metal is generally used for the blade. If the blade is large in size, its weight is increased of course, but even if the blade is small in size, the blade is relatively large unlike normal parts and thus, its weight is apt to be heavy. Therefore, it is impossible to obtain a desired shape simultaneously from one sheet metal using a pressing machine. Thus, a plurality of divided plates divided along bending switch lines of the blade are produced, the divided plates are welded along the bending switch lines of the blade, and a blade having a desired shape is assembled. The welding operation is not difficult when the weld line of the divided plate is a simple straight line, but when the shape of the weld line is complicated or curved, it is difficult to precisely weld even for a skilled welder, producing costs including labor costs is increased, and producing time is increased. As a result, the cost of the product is increased, and deliveries are delayed.
The blade proposed in the patent document 2 has various excellent effects which can not be expected in the conventional blade, but its shape is complicated, and if the attitude of the cutting edge at the time of digging and transporting is taken into consideration and if the welding operation is carried out by a welding robot, high performance motion of the robot is required. Thus, it is necessary to sufficiently study in terms of hardware and software, and it is impossible to develop ideal welding operation at an early stage. It is impossible even for skilled welder to easily carry out high precision welding operation within short time. It is found that the welding strength becomes lower than normal material strength having small thermal hysteresis. To compensate this, welding technique with high precision is required. Since the excavated soil merges with a portion of the bending switch line, if a weld line having inferior wear resistance is used for the bending switch line, there is a possibility that patch-up welding is required relatively within short time.
Generally, main operations of the work machine are digging, transporting and leveling, and it is extremely effective for the work machine to have function capable of carrying out these operations with the same blade because the equipment cost can be reduced. The blade described in the patent document 2 has function of digging, transporting and leveling.
Usually, for the leveling operation of this kind, two points are required, i.e., to flatten the ground while excavating the ground and carry the soil forward and fill in holes during the former operations, and to uniformly level the ground. In the patent document 2, if the blade width of the central front surface portion is increased, the so-called leveling function is enhanced. In the invention, the connecting front surface portion is opened and extended from the central front surface portion rearward as viewed from above, and the end front surface portion is forwardly opened from the right or left connecting front surface portion. Here, although the connecting front surface portion and the end front surface portion also have the leveling function, most of this function relies on the central front surface portion. In the patent document 2 also, it is possible to increase the blade width of the central front surface portion.
In the patent document 2, however, it is also important that soil cut by the cutting edge of the end front surface portion and soil cut by the first cutting edge smoothly merge with each other to largely increase the transporting amount. Therefore, in the patent document 2, as the blade width of the central front surface portion is increased, it becomes necessary to narrow the width of the connecting front surface portion and the end front surface portion as viewed from above.
In order to narrow the width of the connecting front surface portion and the end front surface portion, to reduce resistance force such as digging resistance and transporting resistance, and to largely increase the transporting amount, it is preferable that the length along lower ends of the connecting front surface portion and the end front surface portion is fixed. That is, in order to widen the blade width of the central front surface portion and to secure the necessary length along the lower ends of the connecting front surface portion and the end front surface portion, it is necessary to reduce the bending angle between the connecting front surface portion and the end front surface portion with respect to the digging direction of the central front surface portion as viewed from above. As a result, it naturally becomes necessary to increase the distance between the cutting edge position of the central front surface portion and a supporting point of a lift frame which supports the blade.
If the distance between the cutting edge position of the central front surface portion and the supporting point of the lift frame which supports the blade is increased, an influence of uneven spots on the ground at the time of digging is largely exerted, pitching motion of the vehicle is prone to be generated in the longitudinal direction. As a result, the blade largely swings vertically, stable digging can not be carried out by the central front surface portion, the excavated surface is prone to be uneven, and the ground can not be uniformly flattened. If these factors are taken into consideration, it is necessary to determine the blade width of the central front surface portion while taking the blade widths of the connecting front surface portion and the end front surface portion into consideration. In this invention, the blade width of the central front surface portion is set substantially equal to a gage width which is a distance between centers of right and left running apparatuses, thereby increasing the effective digging force per blade width of the first cutting edge of the central front surface portion, effective digging and transporting can be carried out and it is possible to uniformly level the ground.